In printing works, the printed products from the rotary machine, in particular newspapers and periodicals, are supplied by suitable conveying means to further processing stations (e.g. inserting devices for preliminary and main products, addressing and packaging stations, etc.). In modern, highly automated printing works, where most equipment and sequences are centrally controlled, it is very important to have information at all times and for a large number of strategic points on the number of products which have or have not passed said points (on-line detection and real-time processing of rejects or waste). In view of the high conveying speeds of e.g. 80,000 products per hour, it is also very important to have very precise figures, because even relatively small errors lead in absolute terms to considerable divergences between the actual and the desired quantities and to corresponding economic disadvantages (material losses, superfluous time demands on the printing line and personnel, etc.).
Obviously these needs have already been recognized and numerous processes and apparatuses already exist for counting printed products. One problem which in particular prejudices the measuring accuracy is that the printed products are normally conveyed in a so-called flake or scale flow, i.e. they partly overlap, which makes it much more difficult to recognize, distinguish and determine the individual copies.
Conventional mechanical counting mechanisms generally have a projecting tongue, which is deflected to a certain extent by the upper edges of the printed products conveyed past it and after the passage of the upper edge returns to the inoperative position. The number of deflection movements of said tongue is detected by a counter. The main source of errors for such counting mechanisms is that in the case of printed products, which are provided with a prefold in order to ensure a precisely defined insertion of further printed products, individual printed products, are often counted twice, because the tongue is deflected both by the main fold and also by the prefold. There is also a risk of two or more printed products, which follow one another more closely than they should as a result of an irregularity, cannot be distinguished by the counting mechanism, because the projecting part does not reach its inoperative position between the closely following upper edges. This can also take place if for any reason a printed product projects higher out of the scale flow, so that the movable part is deflected to such an extent that it is no longer deflected by the following printed product. Due to the necessary high pressing pressure between the movable part and the product flow and the resulting friction, incorrect deflection can be caused by even small creases or folds in the printed product. In the case of very thin products, there is a risk of the desired deflection not taking place or at least not being adequate. Although the error rate is often in the 1/1000 range, as stated hereinbefore, it falls beyond the acceptable tolerance limit in high speed processes.
Apart from such mechanical mechanisms, optoelectronic counters are known, which scan the product flow flowing passed e.g. by means of a laser beam and are able to detect the individual printed products on the basis of contrast differences. Quite apart from the fact that the accuracy of such counters can be considerably impaired by marked light/dark differences on the printed product (photographs, etc.), the cost thereof is a particular disadvantage and as a result they are frequently not installed at all the strategically desired points.
It is common to all these known counting mechanisms that they are based on a process, in which the printed products moved passed them are detected at a predetermined, invariable point. However, these statistical counting processes are unable to cope with the constantly varying circumstances of a dynamic process.